Install Postgresql 11.1 on Fedora 29/28, CentOS/RHEL/SL 7.5/6.10

This is guide, howto install PostgreSQL 11.1 database server on Fedora 29/28/27, CentOS/Red Hat (RHEL)/Scientific Linux (SL) 7.5/6.10. This guide uses PostgreSQL own YUM repos, which are always up-to-date and stable releases are available instantly. You can use this guide to install any Postgresql versions, like 12, 11.1, 10.6, 9.6.11, 9.5.15, 9.4.20, and 9.3.25.

Note: If you are upgrading PostgresSQL (from earlier version), then make sure that you backup (dump and copy) your database and configs.